char shift(char prechar,char digit)
{
    return (prechar - 'a')+(digit-'0')+'a';
}
char* replaceDigits(char* s)
{
    int i=0;
    while(s[i]!='\0'&&s[i+1]!='\0')
    {
         s[i+1]=shift(s[i],s[i+1]);
        i=i+2;
    }
    return s;
}